My Strega is flying a lot better then ones I have seen down here and I believe it is because how I built the flaps. There is really some magic about making the flaps thicker and with a rectangular profile (no tapering and no rounding the T.E). My flap is built up, sheeted with 1/16th and it was covered with light weight fiberglass to make it tougher.
Better yet, if you can make flaps using carbon torque tubes like Howard has done it. Making flaps twist resistant, flat and with square T.E. works for me.
If you use the horn that comes with the Strega kit I recommend you make the flaps removable, like shown on the Impact plans. The Brodak horn that came with my kit was very tough to twist and I would not be able to twist the flaps to trim my model if they were not removable.
Martin